Anomalous radiation loss of curved dielectric ridge waveguides

The radiation loss of curved ridge dielectric waveguides can show an oscillatory dependence on radius for the TM-polarisation. This effect is predicted only by a three-dimensional full vectorial analysis and is confirmed experimentally in S-bend dielectric ridge waveguides     

Electromagnetic reflection from a curved dielectric interface

The reflection of a high-frequency electromagnetic field from an arbitrarily curved dielectric interface is considered. The fields are expanded in asymptotic series ofk^{-1}, known as Luneburg-Kline expansions. Based on a ray method the zero- and first-order terms ofk^{-1}of the reflected and transmitted field are evaluated at the interface. Associated with the fields at the interface, effective surface current densities can be used to determine the reflected and transmitted field at points away from the interface, which is done analytically for the reflected far field in the case of plane wave incidence. The result consists of a frequency-independent term, which is related to geometrical optics solution, and a term ofk^{-1}, which is a useful extension of geometrical optics solution in some cases.     

Discrete radiation from curved single-mode fibres

The energy loss and field distribution in a curved single-mode fibre are calculated in terms of the coupling between the fundamental (LP01) mode and the radiation field. In agreement with recent experimental results, it is found that, initially, light travels in a zigzag path around the bend, and radiation is emitted in discrete beams.     

Local form of the radiation condition: application to curved dielectric structures

The form taken by the radiation condition in the local co-ordinate system relevant to a curved radiating structure is not the same as it is at very great distances. It may contain a term that appears as if it were an incoming or growing wave. A detailed analysis has been made of the appropriate form of the condition in the cylindrical and toroidal systems, and has been applied to radiation form curved dielectric slabs and fibres.     

Dissipation loss of mid-infrared radiation in a dielectric waveguide

Dissipation loss of electromagnetic radiation with wavelengths of 20–55 μm was theoretically studied in a three-layer planar dielectric insulating waveguide combined with a heterolaser. It was shown that the dependence of the loss on the waveguide layer thickness behaves differently for different wavelengths in the range of 20–55 μm. The lowest loss (several inverse centimeters) is characteristic of radiation with wavelength λ = 20 μm. The losses increase with the wavelength and reach a value of 150 cm^-1 at λ = 40 μm, which is almost independent of the waveguide layer thickness. For electromagnetic radiation with λ = 50 and 55 μm, a sharp (hundreds of times) decrease in the loss with an increase in the waveguide layer thickness is observed.     

Reducing radiation loss of tilts in dielectric optical waveguides

It is proposed to reduce the radiation loss of an optical wave-guide tilt by increasing the refractive index on the inner side, or by decreasing it on the outer side of the tilt By microwave model experiments it is shown that the method proposed is effective.     

Multiple dielectric slabs in waveguide cell

The transverse resonance method is used to evaluate the effective dielectric constant of a material present in the form of multiple slabs that partially fill a waveguide cell. It is shown that the commonly-used linear relationship for the effective dielectric constant of a mixture of dielectrics holds good to better than 1% accuracy only when the slabs are, in general, of a width each less than 5% of the wavelength in the dielectric. Alternative mixture equations with empirical terms are also presented     

Pattern of radiation from dielectric tapers

The `radiation? from a dielectric taper is still within the vicinity of the taper core. The dominant reason for the radiation loss is the mismatch between the fields in the ends of the taper.     

TM modes guided by nonlinear dielectric slabs

Propagation of a TM₀ mode in a Kerr-type nonlinear dielectric slab is investigated. The exact analytical expression of E ²(x), E²=E_x²+E_Z ², the decoupled linear differential equation and its equivalent Volterra integral equation of E_x, and the eigenvalue equation of propagation constant β are presented. Finally, an example of approximate analytical solutions obtained by the method of successive approximation is given     

Microwave shielding effectiveness of EC-coated dielectric slabs

Correct formulas for the microwave shielding effectiveness (SE ) of a thin metallic layer deposited on top of a dielectric slab are derived. For coatings much thinner than the skin depth, the following holds: (a) in a half-wave geometry, SE is a function of a sheet resistance only, SE (in dB)=20×log(1+188.5/R_s) if R_s is in ohms per square; (b) in a quarter-wave geometry, SE (in dB)=20×log[(1+ε_r)/(2√ε _r)+188.5/(√ε_rR_s)], where ε_r refers to the dielectric constant of the substrate. These formulas provide upper and lower limits for the effective shielding performance of an electroconductive coated dielectric slab     

Electromagnetic scattering from 3-D curved dielectric bodies usingtime-domain integral equations

A boundary integral equation (BIE) approach is developed to calculate transient scattering from dielectric bodies. The treatment is directly in terms of the E and H fields rather than magnetic and electric currents. It employs curvilinear (quadratic) modeling, which allows accurate representation of arbitrarily shaped curved bodies. The treatment is isoparametric with the same quadratic representation of the spatial field variation and with the temporal variation modeled by similar quadratic elements. Integration employs high-order Gaussian quadrature with special treatment of the singular and hypersingular integrals that arise. The treatment is implicit, requiring the solution of a sparse matrix equation at each timestep. This adds only trivially to the cost at each timestep and, by freeing the timestep from the constraint that it be smaller than the smallest nodal spacing, can greatly reduce the number of timesteps that must be employed. Additionally, it produces stable results without resort to the averaging processes proposed elsewhere. Example calculations of scattering from a sphere, a cube, and an almond are presented and compared with earlier published transient results and with results from a frequency domain treatment. Good agreement and improved accuracy is found     

FDTD analysis of dielectric resonators with curved surfaces

In this paper, the finite-difference time-domain (FDTD) method is applied to calculate the resonant frequency of dielectric resonators (DRs) with curved surface. The contour-path integral FDTD (CFDTD) is modified to deal with the curved surface of the dielectric body while the traditional rectangular cells are maintained. Results are compared with theoretical values and staircase approximation, and show that the present method is more accurate than the staircase approximation     

Loss reduction in curved dielectric optical slab waveguide

Formulas of the pure bending loss and the transition loss valid for TM modes in dielectric optical slab waveguides are presented. The characteristic of the total transmission loss of a step-index slab waveguide containing a circular bend having an asymmetric waveguide structure are analysed numerically by applying derived loss formulas. It is found that the features of the total transmission loss of TM modes are closely analogous to those of TE modes except for small discrepancies in the numerical values.     

FREQUENCY-DOMAIN METHOD FOR RECONSTRUCTION OF THE PARAMETERS OF DIELECTRIC SLABS

The complex parameters of dielectric slabs can be reconstructed according to thescattered field data if the slabs are illuminated by a harmonic electromagnetic wave and thescattered field is measured.This paper describes a method for reconstruction of the parametersof single or double inhomogeneous lossy dielectric slabs.The numerical results are demonstrated.     

光纤中小损耗对超高斯型脉冲传输特性的影响

本文从MNLS方程出发,采用变分法,导出了在小损耗情况下超高斯脉冲参数随传输距离的演化方程组及其解,讨论了小损耗对光纤中超高斯脉冲传输特性的影响。     

Discrete radiation from curved single-mode fibres: a comparison of theories

An apparent discrepancy between coupled-mode and `whispering-gallery? theories for the radiation of discrete beams from curved single-mode fibres is resolved. It is shown that the two formally different approaches are in very good agreement with each other in predicting the periodicity of the radiation.     

Dielectric tapers with curved axes and no loss

An "exact" theory is developed for the design of single or muitimode dielectric tapers of arbitrary cross sections and straight or curved axes that have the unique property of guiding with no conversion either to other guided modes or to radiation modes. This remarkably simple theory encompasses a very wide gamut of strictly adiabatic tapers: some very simple, such as linear tapers with straight axes, some very sophisticated, such as directional couplers made of noncoplanar guides tapered and curved differently.     

太赫兹频段一维介质光子晶体中的史密斯-帕塞尔辐射特性模拟

基于Smith-Purcell(SP)效应,采用粒子模拟的方法探讨了电子束团激发一维介质光子晶体中的SP辐射特性.模拟研究了单个束团激发一维介质圆柱光子晶体产生的SP辐射现象,并对周期束团激发的THz频段的相干SP辐射进行了模拟分析.研究表明,提高介质的相对介电常数和增加光子晶体的层数都可使辐射强度增加,选择合适的参数能够有效地增强THz频段的相干SP辐射强度.     

Lateral wave contribution to the radiation from a dielectric halfmedium

Two methods are presented for the computation of the radiation at microwave frequencies in a thin dielectric medium from a source located in a dense dielectric medium. One is based on geometrical optics and the other on physical optics. The geometrical optics approach encounters some difficulties in the evaluation of the radiation in the thin dielectric medium near grazing-incidence condition, due to excitation of a lateral wave, which is not taken in consideration by this approach. The physical optics method, which considers the lateral wave contribution, approaches this problem successfully and gives a better approximation of the radiated field near grazing. Numerical results, which compare the two methods, and experimental data are offered to validate the theoretical approach